In the Return of the King, there are the orcs that come from Minas Morgul. Were they produced in Mordor and transferred there, or were they actually created in Minas Morgul by the Witch King?
The origin of the orcs is in doubt, what is not in doubt is that no, the witch king did not create orcs.
The Silmarillion tells us that orcs where corrupt elves, tortured in the pits of Angband by Morgoth, who did not have the power to create new life, only to corrupt.
But of those unhappy ones who were ensnared by Melkor little is known of a certainty. For who of the living has descended into the pits of Utumno, or has explored the darkness of the counsels of Melkor? Yet this is held true by the wise of Eressëa, that all those of the Quendi who came into the hands of Melkor, ere Utumno was broken, were put there in prison, and by slow arts of cruelty were corrupted and enslaved; and thus did Melkor breed the hideous race of the Orcs in envy and mockery of the Elves, of whom they were afterwards the bitterest foes. For the Orcs had life and multiplied after the manner of the Children of Ilúvatar; and naught that had life of its own, nor the semblance of life, could ever Melkor make since his rebellion in the Ainulindalë before the Beginning: so say the wise.
Ref: The Silmarillion: OF THE COMING OF THE ELVES AND THE CAPTIVITY OF MELKOR
Orcs (after they were "created" by Morgoth) bred like humans or other mammals do - from a male and female conceiving a baby. What Sauron and Saruman could do, is to breed them selectively (with some use of magic, perhaps) to "create" more powerful and more resilient orcs.
In Saruman's case, he interbred orcs with humans, creating orc-men or goblin-men. One descendant of such evil project appeared at the Inn of the Prancing Pony, that squint-eyed stranger that was spying on the Hobbits.
Sauron reportedly created a stronger and more resilient breed, some of which were stationed in Minas Morgul. The Witch King didn't have anything to do with the breeding, he was simply their chief general.